Well, i dont think seno likes natsuki. He just found out natsuki liked him, and stumbled upon a scene where natsuki was being romantic. He saw what was happening and simply thought that could've been me. However, he quickly came to the realization that it wouldn't have been possible because there was no way he could be that way with natsuki. He probably deduced his personality or his sexuality wouldn't have allowed for it. And what seno and natsuki share is uniquely their own.
I wonder it that makes sense?? Like I have had moments when I thought that could've been me, but quickly realize there was no way it could be me with the way I am now.

Now that he is with seno, the other guy started to like him? what did he mean by i´m not seno???? wtf loving someone for so long and once u move on they realize their feeling lol